Processes for in-situ annealing of TMR sensors

ABSTRACT

A method in one embodiment includes applying a current to a lead of a tunneling magnetoresistance sensor for inducing joule heating of the lead or a heating layer, the level of joule heating being sufficient to anneal a magnetic layer of the sensor; and maintaining the current at the level for an amount of time sufficient to anneal the tunneling magnetoresistive (TMR) sensor. Additional systems and methods are also presented.

RELATED APPLICATIONS

This application is a divisional of U.S. Pat. No. 8,331,064, filed Apr.18, 2008; which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to magnetic sensor annealing, and moreparticularly, this invention relates to annealing a TunnelingMagnetoresistance (TMR) sensor.

BACKGROUND OF THE INVENTION

In magnetic storage systems, data is read from and written onto magneticrecording media utilizing magnetic transducers commonly. Data is writtenon the magnetic recording media by moving a magnetic recordingtransducer to a position over the media where the data is to be stored.The magnetic recording transducer then generates a magnetic field, whichencodes the data into the magnetic media. Data is read from the media bysimilarly positioning the magnetic read transducer and then sensing themagnetic field of the magnetic media. Read and write operations may beindependently synchronized with the movement of the media to ensure thatthe data can be read from and written to the desired location on themedia.

An important and continuing goal in the data storage industry is that ofincreasing the density of data stored on a medium. For tape storagesystems, that goal has lead to increasing the track density on recordingtape, and decreasing the thickness of the magnetic tape medium. However,the development of small footprint, higher performance tape drivesystems has created various problems in the design of a tape headassembly for use in such systems.

TMR sensors are used as readers in magnetic storage systems such as harddisk drives (HDD) and could be used in tape drives. Some TMR sensorshave been shown to have an intrinsic defect which is caused by stressvoltages. Particularly, both intrinsic and extrinsic breakdown behaviorshave been observed. The intrinsic breakdown is characterized by anabrupt resistance drop in the TMR at the failure voltage, whileextrinsic breakdown is characterized by a gradual drop in the resistanceof the TMR.

SUMMARY OF THE INVENTION

A method in one embodiment includes applying a current to a lead of atunneling magnetoresistance sensor for inducing joule heating of thelead or a heating layer, the level of joule heating being sufficient toanneal a magnetic layer of the sensor; and maintaining the current atthe level for an amount of time sufficient to anneal the tunnelingmagnetoresistive (TMR) sensor.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a tape drive system, which may include a magnetic head asrecited above, a drive mechanism for passing a magnetic medium (e.g.,recording tape) over the magnetic head, and a controller electricallycoupled to the magnetic head.

Other embodiments of the present invention will become apparent from thefollowing detailed description, which, when taken in conjunction withthe drawings, illustrate by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a simplified tape drive systemaccording to one embodiment.

FIG. 2 illustrates a side view of a flat-lapped, bi-directional,two-module magnetic tape head according to one embodiment.

FIG. 2A is a tape bearing surface view taken from Line 2A of FIG. 2.

FIG. 2B is a detailed view taken from Circle 2B of FIG. 2A.

FIG. 2C is a detailed view of a partial tape bearing surface of a pairof modules.

FIG. 3 is a system diagram of an illustrative system having a tunnelingmagnetoresistance (TMR) sensor according to one embodiment.

FIG. 4 is a flow diagram of a method for annealing a TMR sensoraccording to one embodiment.

FIG. 5 is a system diagram of an illustrative system having a TMR sensoraccording to one embodiment.

FIG. 6A is an electrical schematic of the current flow for a TMR sensorduring annealing by Joule heating currents according to the method shownin FIG. 5.

FIG. 6B is an electrical schematic of the current flow for a TMR sensorduring annealing by Joule heating currents according to the method shownin FIG. 7.

FIG. 7 is a system diagram of an illustrative system having a TMR sensoraccording to one embodiment.

FIG. 8 is a system diagram of an illustrative system having a TMR sensoraccording to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof.

In one general embodiment, a method includes applying a current to alead of a tunneling magnetoresistance sensor for inducing joule heatingof the lead or a heating layer, the level of joule heating beingsufficient to anneal a magnetic layer of the sensor; and maintaining thecurrent at the level for an amount of time sufficient to anneal thetunneling layer and/or the magnetic layers of the sensor. The leadstructure(s) is (are) connected in a circuit such that the joule heatingcurrent passes through a thin film metal layer rather than through thetunnel junction.

In another general embodiment, a system includes a first lead coupled toone end of a tunneling magnetoresistance sensor stack; a second leadcoupled to another end of the sensor stack; and a third lead coupled tothe first lead, the third lead being selectively coupleable to a ground,and the first lead is selectively coupled to a voltage (current) source,wherein a current passing through the first lead to the third lead whenthe third lead is coupled to the ground does not significantly traversethe sensor stack, wherein the first and third leads are characterized inthat a current applied to the first lead at a predetermined level whenthe third lead is coupled to the ground induces joule heating of thefirst lead or a heating layer coupled to the first and third leads, thejoule heating applied for a predetermined amount of time beingsufficient to anneal a magnetic layer of the sensor.

In another general embodiment, a system includes a first lead coupled toone end of a tunneling magnetoresistance sensor stack, and where thefirst lead is selectively coupled to a voltage (current) source; asecond lead coupled to another end of the sensor stack, and where thesecond lead is also selectively coupled to a voltage (current) source; athird lead coupled to the first lead, the third lead being selectivelycoupleable to a ground; and a fourth lead coupled to the second lead,the fourth lead being selectively coupleable to the ground. The firstand third leads are characterized in that a current applied to the firstlead at a predetermined level when the third lead is coupled to theground induces joule heating of the first lead or a heating layercoupled to the first and third leads, wherein the second and fourthleads are characterized in that a current applied to the second lead ata predetermined level when the fourth lead is coupled to the groundinduces joule heating of the second lead or a heating layer coupled tothe second and fourth leads, the combined joule heating generated for apredetermined amount of time being sufficient to anneal a magnetic layerof the sensor. The connections are such that the magnetic fieldgenerated within the Tunnel Junction (TJ) stack from the currentspassing through the first and third leads opposes the magnetic fieldgenerated within the TJ stack from the second and fourth leads. In thisconfiguration the second and the fourth leads are aligned as mirrorimages of the first and third leads respectively.

One reason for the above mentioned alignment is to minimize the magneticfields within the TMR. Another important reason is to minimize thevoltage differential across the oxide, tunneling, layer of the TMR.

In yet another general embodiment, a system includes a tunnelingmagnetoresistance sensor; a heating layer for heating the sensor, theheating layer being external to a thin film stack of the sensor; andleads coupled to the heating layer, wherein the heating layer ischaracterized in that a current applied thereto at a predetermined levelfor a predetermined amount of time anneals a magnetic layer of thesensor.

FIG. 1 illustrates a simplified tape drive 100 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 1, it should be noted that the embodiments described herein may beimplemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 areprovided to support a tape 122. One or more of the reels may form partof a removable cassette and are not necessarily part of the system 100.The tape drive, such as that illustrated in FIG. 1, may further includedrive motor(s) to drive the tape supply cartridge 120 and the take-upreel 121 to move the tape 122 over a tape head 126 of any type.

Guides 125 guide the tape 122 across the tape head 126. Such tape head126 is in turn coupled to a controller assembly 128 via a cable 130. Thecontroller 128 typically controls head functions such as servofollowing, writing, reading, etc. The cable 130 may include read/writecircuits to transmit data to the head 126 to be recorded on the tape 122and to receive data read by the head 126 from the tape 122. An actuator132 controls position of the head 126 relative to the tape 122.

An interface may also be provided for communication between the tapedrive and a host (integral or external) to send and receive the data andfor controlling the operation of the tape drive and communicating thestatus of the tape drive to the host, all as will be understood by thoseof skill in the art.

By way of example, FIG. 2 illustrates a side view of a flat-lapped,bi-directional, two-module magnetic tape head 200 which may beimplemented in the context of the present invention. As shown, the headincludes a pair of bases 202, each equipped with a module 204, and fixedat a small angle α with respect to each other. The bases are typically“U-beams” that are adhesively coupled together. Each module 204 includesa substrate 204A and a closure 204B with a gap 206 comprising readersand/or writers situated therebetween. In use, a tape 208 is moved overthe modules 204 along a media (tape) bearing surface 209 in the mannershown for reading and writing data on the tape 208 using the readers andwriters. The wrap angle θ of the tape 208 at edges going onto andexiting the flat media support surfaces 209 are usually between ⅛ degreeand 4½ degrees.

The substrates 204A are typically constructed of a wear resistantmaterial, such as a ceramic. The closures 204B made of the same orsimilar ceramic as the substrates 204A.

The readers and writers may be arranged in a piggyback configuration.The readers and writers may also be arranged in an interleavedconfiguration. Alternatively, each array of channels may be readers orwriters only. Any of these arrays may contain one or more servo readers.

FIG. 2A illustrates the tape bearing surface 209 of one of the modules204 taken from Line 2A of FIG. 2. A representative tape 208 is shown indashed lines. The module 204 is preferably long enough to be able tosupport the tape as the head steps between data bands.

In this example, the tape 208 includes 12-22 data bands, e.g., with 16data bands and 17 servo tracks 210, as shown in FIG. 2A on a one-halfinch wide tape 208. The data bands are defined between servo tracks 210.Each data band may include a number of data tracks, for example 96 datatracks (not shown). During read/write operations, the elements 206 arepositioned within one of the data bands. Outer readers, sometimes calledservo readers, read the servo tracks 210. The servo signals are in turnused to keep the elements 206 aligned with a particular track during theread/write operations.

FIG. 2B depicts a plurality of read and/or write elements 206 formed ina gap 218 on the module 204 in Circle 2B of FIG. 2A. As shown, the arrayof elements 206 includes, for example, 16 writers 214, 16 readers 216and two servo readers 212, though the number of elements may vary.Illustrative embodiments include 8, 16, 32, and 40 elements per array206. A preferred embodiment includes 16 readers per array and/or 16writers per array. The more the elements in an array, the higher thedata rate for a given tape speed. The choice of the exact number ofelements required is, among other issues, a trade off of cost ofelectronics per element, the possibility in defects, whereby 1 defectiveelements renders the array useless, the data rate transfer required.While the readers and writers may be arranged in a piggybackconfiguration as shown in FIG. 2B, the readers 216 and writers 214 mayalso be arranged in an interleaved configuration. Alternatively, eacharray of elements 206 may be readers or writers only, and the arrays maycontain one or more servo readers 212. As noted by considering FIGS. 2and 2A-B together, each module 204 may include a complementary set ofelements 206 for such things as bi-directional reading and writing,read-while-write capability, backward compatibility, etc.

FIG. 2C shows a partial tape bearing surface view of complimentarymodules of a magnetic tape head 200 according to one embodiment. In thisembodiment, each module has a plurality of read/write (R/W) pairs in apiggyback configuration formed on a common substrate 204A and anoptional electrically insulative layer 236. The writers, exemplified bythe write head 214 and the readers, exemplified by the read head 216,are aligned parallel to a direction of travel of a tape mediumthereacross to form an R/W pair, exemplified by the R/W pair 222.

Several R/W pairs 222 may be present, such as 8, 16, 32 pairs, etc. TheR/W pairs 222 as shown are linearly aligned in a direction generallyperpendicular to a direction of tape travel thereacross. However, thepairs may also be aligned diagonally, etc. Servo readers 212 arepositioned on the outside of the array of R/W pairs, the function ofwhich is well known.

Generally, the magnetic tape medium moves in either a forward or reversedirection as indicated by arrow 220. The magnetic tape medium and headassembly 200 operate in a transducing relationship in the mannerwell-known in the art. The piggybacked MR head assembly 200 includes twothin-film modules 224 and 226 of generally identical construction.

Modules 224 and 226 are joined together with a space present betweenclosures 204B thereof (partially shown) to form a single physical unitto provide read-while-write capability by activating the writer of theleading module and reader of the trailing module aligned with the writerof the leading module parallel to the direction of tape travel relativethereto. When a module 224, 226 of a piggyback head 200 is constructed,layers are formed in the gap 218 created above an electricallyconductive substrate 204A (partially shown), e.g., of AlTiC, ingenerally the following order for the R/W pairs 222: an insulating layer236, a first shield 232 typically of an iron alloy such as NiFe(permalloy), CZT or Al—Fe—Si (Sendust), a sensor 234 for sensing a datatrack on a magnetic medium, a second shield 238 typically of anickel-iron alloy (e.g., 80/20 Permalloy), first and second writer poletips 228, 230, and a coil (not shown).

The first and second writer poles 228, 230 may be fabricated from highmagnetic moment materials such as 45/55 NiFe. Note that these materialsare provided by way of example only, and other materials may be used.Additional layers such as insulation between the shields and/or poletips and an insulation layer surrounding the sensor may be present.Illustrative materials for the insulation include alumina and otheroxides, insulative polymers, etc.

Another type of magnetic recording system is a hard disk drive system.Such a system generally includes a slider having a magnetic head with asensor and a writer. The slider flies above a rotating magnetic disk,and is positioned over the appropriate data track on the disk by anactuator. Typically, a controller is present for managing thepositioning and operation of the head.

FIG. 3 illustrates an illustrative system 300 having a tunnelingmagnetoresistance (TMR) sensor (also known as a Magnetic Tunnel Junction(MTJ) sensor) that may be implemented in any of the embodimentsdescribed above. It should be noted, however, that the sensor 300 may beimplemented in any type of system or environment in which magneticsensors can be employed.

A TMR device comprises two ferromagnetic layers separated by a thin,electrically insulating, tunnel barrier layer. The tunnel barrier layeris sufficiently thin that quantum-mechanical tunneling of chargecarriers occurs between the ferromagnetic layers. The tunneling processis electron spin dependent, which means that the tunneling currentacross the junction depends on the spin-dependent electronic propertiesof the ferromagnetic materials and is a function of the relativeorientation of the magnetizations of the two ferromagnetic layers. In atypical TMR sensor, one ferromagnetic layer (pinned layer) has itsmagnetization fixed, or pinned, and the other ferromagnetic layer (freelayer) has its magnetization free to rotate in response to an externalmagnetic field, such as that emanating from the recorded magnetictransitions written to the recording medium (the signal field). When anelectric potential (voltage) is applied across the two ferromagneticlayers, the sensor resistance is a function of the tunneling currentacross the insulating layer between the ferromagnetic layers. Since thetunneling current that flows perpendicularly through the tunnel barrierlayer depends on the relative magnetization directions of the twoferromagnetic layers, recorded data can be read from a magnetic mediumwhereby the magnetic flux emanating from the media causes a change ofdirection of magnetization of the free layer, which in turn causes achange in the resistance of the MTJ sensor and a corresponding change inthe sensed current or voltage.

With continued reference to FIG. 3, the TMR sensor comprises a firstelectrode 304, a second electrode 302, and a tunnel barrier layer 315,typically of a metal oxide such as, but not limited to, AlO_(x),MgO_(x), etc. The first electrode 304 comprises a pinned layer (pinnedferromagnetic layer or reference layer) 320, an antiferromagnetic (AFM)layer 330, and a seed layer 340. The magnetization of the pinned layer320 is fixed through exchange coupling with the AFM layer 330. Thesecond electrode 302 comprises a free layer (free ferromagnetic layer)310 and a cap layer 305. The free layer 310 is separated from the pinnedlayer 320 by a nonmagnetic, electrically insulating tunnel barrier layer315. In the absence of an external magnetic field, the free layer 310has its magnetization oriented in the direction shown by arrow 312, thatis, generally perpendicular to the magnetization direction of the pinnedlayer 320 shown by arrow 322 (tail of an arrow pointing into the planeof the paper). The magnetization orientation is, in part, determined bythe hard bias magnets 385 oriented on either side of the MTJ. A firstlead 360 and a second lead 365 formed in contact with first electrode304 and second electrode 302, respectively, provide electricalconnections for the flow of sensing current I_(s) from a current source370 to the TMR sensor 300. The first 360 and second 365 leads could alsoattach to the ends of the first 304 and second 302 electrodes ratherthan forming additional layers parallel to the first and secondelectrodes.

Because the sensing current is perpendicular to the plane of the sensorlayers, the TMR sensor is known as a current-perpendicular-to-plane(CPP) sensor. A signal detector 380, typically including a recordingchannel such as a partial-response maximum-likelihood (PRML) channel,connected to the first and second leads 360 and 365 senses the change inresistance due to changes induced in the free layer 310 by the externalmagnetic field.

It should be noted that various embodiments of the present invention maydeviate from the system shown in FIG. 3. For example, variousembodiments may include more or fewer layers, other layers, hard biaslayers flanking the sensor stack, etc.

As noted above, some TMR sensors can be degraded by stresses and eventssuch as current pulses and Electrostatic Discharge (ESD) events. Whilenot wishing to be bound by any theory, it is believed that one method ofTMR degradation is a process of trap generation and trapped chargeaccumulation. The resistance decrease trend before hard breakdown is asymptom of this trap development. Physically, under high current/voltagestress, the broken bonds (both bulk and interfatial) may act as electrontraps, which result in a reversible damage to the tunneling propertiesof the oxide.

Considering the trapping effect during voltage stress, an apparentdecrease of the effective barrier thickness is related to trapgeneration in barrier probably, so called “trap-assisted tunneling”(TAT) make more electrons to tunnel through ultra thin barrier with onemore steps. Tunneling current (conductivity) is sensitive to thethickness change, i.e., the conductivity of barrier will be determinedby the longest distance from trap to either electrode, TAT inside onebarrier can increase the tunneling current (conductivity) obviously. So,it is one possible explanation of the observed “slightly increasedconductivity” after electrical stress, which can be parameterized by adecrease in the effective barrier thickness. The trap state availablefor electrons to tunnel, or the charge state of trap in barrier canmodify the form of the barrier potential, giving new effective barriervalues after electrical stress. The apparent increase of the barrierheight is probably a result of trapped negative charge (electrons)accumulation inside the barrier.

However, the degradation of the TMR sensor functionality associated withcharge trapping can be reversed by annealing the sensor at apredetermined temperature for a predetermined amount of time.Particularly, after annealing, the TMR recovers to about its initialstate, presumably by releasing the trapped charges.

While the TMR sensor may be annealed in an oven, there are at least twoproblems with annealing in an oven. One problem is that annealing in anoven requires removing the part from the manufacturing line or from thedrive to do the annealing. This is time consuming and costly. Anotherproblem is that, for a head used in tape drives, a closure is usuallyglued onto the head. For most glues, the annealing temperature is wellabove the glass transition of the adhesive used to glue the closure andso the closure will move, making the parts unusable. Therefore, it wouldbe desirable to generate the annealing heat from within the head.

FIG. 4 illustrates a method 400 for annealing a TMR sensor according toone embodiment. As an option, the present method 400 may be implementedin the context of the functionality and architecture of FIGS. 1-3.However, method 400 may be carried out in any desired environment. Itshould be noted that the aforementioned definitions may apply during thepresent description.

In optional operation 402, the thermodynamic parameters of the TMRsensor are characterized to determine the power and time duration ofJoule heating required to anneal the TMR sensor into a recovered state.

In optional operation 404, the thermal characteristics of the TMRsensor/Joule heating system are characterized to understand therelationship of power (current) through the Joule heating elementsrequired to achieve a given temperature for a given time at the portionof the TMR sensor required to be recovered. Note that the informationdetermined in operations 402 or 404 may already be known for aparticular type of TMR sensor, and so some approaches need not performthese steps.

With continued reference to FIG. 4, in operation 406, a current isapplied to a lead of the TMR sensor for inducing joule heating of thelead or a heating layer (e.g., heating element), the level of jouleheating being sufficient to anneal a magnetic layer (e.g., pinned layer320, FIG. 3) of the sensor, e.g., such that the combination of the powerand a predetermined or dynamically-determined time duration aresufficient to anneal the sensor into a recovered state. Note that thelead may be a unitary structure, or a combination of components such asa conductive via and a magnetic shield or hard bias layer.

The currents used for the annealing could be either lower values andlonger times (in the regime of seconds or minutes or hours), or could behigher currents to achieve annealing in shorter times such asmillisecond or microsecond or nanosecond time regimes.

In operation 408, the current is maintained at the level for an amountof time sufficient to anneal the magnetic layer of the sensor. Ingeneral, the heating is below that which would damage other parts of thehead, but high enough to anneal the structure. For example, the currentis sufficient to heat the magnetic layer to between about 100° C. andabout 300° C. for between about 30 seconds and about 5 hours at acurrent of between about 1 and about 100 mA. In one illustrativeapproach, for a TMR sensor having a MgO barrier of about ˜5.5 Å thick,the current is sufficient to heat the magnetic layer to about 120° C.for about 2 hours, which should be sufficient to anneal such a sensor.Those skilled in the art will appreciate that the time and annealingtemperature may be tuned to the sensor, and so the ranges listed aboveare not to be construed as limiting.

Accordingly, because Joule heating is performed, the annealing may beperformed in situ in the drive having the TMR sensor installed therein.

In particularly preferred approaches, no external magnetic field isapplied to the magnetic layer during the annealing. Any magnetic fieldcreated by the current passing through the leads is not considered anexternal magnetic field.

FIG. 5 depicts an illustrative system 500 having a TMR sensor 502according to one embodiment. As an option, the present system 500 may beimplemented in the context of the functionality and architecture ofFIGS. 1-4. However, the system 500 may be implemented in any desiredenvironment. It should be noted that the aforementioned definitions mayapply during the present description.

In general, TMR sensors can not carry significant current levels throughthe tunnel junction to self heat sufficiently to anneal out defects. Onereason for low current levels is damage to the TJ either from intrinsicor extrinsic causes. For example, extant disk drives use TMR sensorswith oxides that are damaged by 0.5 to 1 V across the TJ. Such sensorshave resistances of the order of 300 ohms, so the current levels thatresult in damage are of the order of 1.6 or 3.3 mA.

As shown in FIG. 5, the system includes a first lead 506 coupled to oneend of a tunneling magnetoresistance sensor stack 502. The first lead506 is selectively coupled to a voltage/current source 516. A secondlead 508 is coupled to another end of the sensor stack. A third lead 510is coupled to the first lead, the third lead being selectivelycoupleable to a ground 512. During Joule heating, lead 506 is coupled toa voltage/current source while lead 510 is coupled to ground andcurrent, is passed through the first lead to the third lead. Since lead508 is floating, current does not significantly traverse the sensorstack. Note that there may or may not be some current leakage across thesensor stack. To minimize current flow through lead 508, during Jouleheating, lead 508 should be disconnected from external contacts.

The first and third leads are characterized in that a current applied tothe first lead at a predetermined level when the third lead is coupledto the ground induces joule heating of the first lead or a heating layercoupled to the first and third leads. When the joule heating is appliedfor a predetermined amount of time, it is sufficient to anneal amagnetic layer of the sensor. An example of a heating layer is a thinmetal film.

As shown, the first lead is also used for applying a sense current tothe sensor. However, in some embodiments, the first lead may not be usedfor applying a sense current to the sensor.

While the direction that the current is applied is not critical, it maybe beneficial to use the magnetic field created by the current flow toassist in the annealing. Those skilled in the art could, if necessary,choose the direction of current flow appropriately to create theappropriate magnetic field. For example, in FIG. 5, if the direction ofcurrent flow is from lead 506 to lead 510, then a magnetic field will becreated in the stack pointing into the page. If the direction of currentflow is reversed to go from lead 510 to lead 506, then a magnetic fieldwill be created in the stack pointing out of the page. An example of adesire to orient the current-flow generated magnetic field would be togenerate a field in the pinned-AFM layers in a direction that itsupports the preferred alignment of the magnetization in those layers.

Though the current flow through the stack should be minimal, under theembodiment shown in FIG. 5, some current flow will pass through thestack. FIG. 6A shows a simplified example of this. In FIG. 6A, the stackis represented as three equal resistors 605, 610 and 615, all of valueR. The total resistance across the TMR, then is given by R/3. The metalconnecting leads 506 and 510 and along 508 under the TJ are assumed tohave identical resistance properties, and are divided into two aboutequal resistors 620 and 625 of resistance r. Resistor 620 connects thetop ends of resistors 605 and 610, while resistor 625 connects the topends of resistors 610 and 615 The bottom lead has about two equalresistor 630 and 635. Resistor 630 connects the bottom ends of resistors605 and 610, while resistor 635 connects the bottom ends of resistors610 and 615. When a voltage source of value V is connected to lead 506,and a ground source is connected to lead 510, current flows between 506and 510 of level I_(Joule)=V/2r. A leakage current will flow ofI_(leak)˜V/2R through resistor 605 while a leakage currentI_(leak)˜−V/2R will flow through resistor 615. If R˜1000Ω, and r˜10Ω,then I_(leak)/I_(Joule) will be about 1%, so this may be ok. If, on theother hand, r˜100 W, the I_(leak)/I_(Joule) will be about 10%.Furthermore, if the voltage level V/2 is of the order of the damagethreshold for the tunnel junction, then this embodiment may not beadvantageous.

In some instances, it may be beneficial to reduce the voltagedifferential across the sensor stack.

Accordingly, in one approach, a current is also applied to the secondlead. In a further approach, described generally with reference to FIG.7, current can pass along both sides of the sensor.

FIG. 7 depicts an illustrative system 700 having a TMR sensor 502according to another embodiment. As an option, the present system 700may be implemented in the context of the functionality and architectureof FIGS. 1-4. However, the system 700 may be implemented in any desiredenvironment. It should be noted that the aforementioned definitions mayapply during the present description.

As shown in FIG. 7, the system includes a first lead 506 coupled to oneend of a tunneling magnetoresistance sensor stack 502. A second lead 508is coupled to another end of the sensor stack. A third lead 510 iscoupled to the first lead A fourth lead 514 is coupled to the secondlead. The third and fourth leads being selectively coupleable togetherto the ground 512 using switches 518. The first and third leads arebeing selectively coupleable together to a voltage/current source 516using switches 518. The first and third leads are characterized in thata current applied to the first lead at a predetermined level when thethird lead is coupled to the ground induces joule heating of the firstlead or a heating layer coupled to the first and third leads. The secondand fourth leads are characterized in that a current applied to thesecond lead at a predetermined level when the fourth lead is coupled tothe ground induces joule heating of the second lead or a heating layercoupled to the second and fourth leads. The combined joule heatinggenerated for a predetermined amount of time being sufficient to anneala magnetic layer of the sensor.

While the voltage applied to the first and third leads 506, 510 may bedifferent, in the preferred embodiment, they are the same. As describedabove, when the same voltage level is desired, the first and third leads506, 510 are tied together to get the same voltage. If a differentvoltage is desired across leads 508 to 518 than across leads 506 and510, then the two leads would not be tied together.

A schematic to explain the minimization of leakage current and ofvoltage differential across the TJ is shown in FIG. 6B for the case whenthe voltage drop cross leads 508 to 518 is equal to that across leads506 and 510. In FIG. 6B, the stack is represented as three equalresistors 605, 610 and 615, all of value R. The total resistance acrossthe TMR, then is given by R/3. The metal connecting leads 506 and 510and 508 to 514 under the TJ are assumed to have identical resistanceproperties, and are divided into two equal resistors 620 and 625 ofresistance r. Resistor 620 connects the top ends of resistors 605 and610, while resistor 625 connects the top ends of resistors 610 and 615.The bottom lead has two equal resistors 630 and 635. Resistor 630connects the bottom ends of resistors 605 and 610, while resistor 635connects the bottom ends of resistors 610 and 615. When a voltage sourceof value V is connected to leads 506 and 508, and a ground source isconnected to leads 510 and 514, current flows between 506 and 510 oflevel I_(Joule)=V/2r and an equal current flows between 508 and 514 oflevel I_(Joule)=V/2r. With this symmetric circuit, no leakage currentshould flow through resistors 605, 610 or 615. Furthermore, there shouldbe no voltage drop across either resistor: 605, 610 or 615.

FIG. 8 illustrates an embodiment 800 in which the heating is generatedexternally of the sensor stack. As an option, the present system 800 maybe implemented in the context of the functionality and architecture ofFIGS. 1-6. However, the system 800 may be implemented in any desiredenvironment. It should be noted that the aforementioned definitions mayapply during the present description.

As shown, the system 800 includes a TMR sensor 502, a heating layer 520for heating the sensor, the heating layer being external to a thin filmstack of the sensor, and preferably electrically isolated therefrom.Leads 522, 524 are coupled to the heating layer. The heating layer ischaracterized in that a current applied thereto at a predetermined levelfor a predetermined amount of time anneals a magnetic layer of thesensor. By using a Joule heating element which is electrically isolatedbut thermally connected, such as by using a thin electrical insulatinglayer, one could avoid the potential of dielectric breakdown or othervoltage induced damage across the TJ.

The heating layer may be any type of heating layer, such as a thermalelement, etc.

The invention can take the form of an entirely hardware embodiment, anentirely software embodiment or an embodiment containing both hardwareand software elements. In a preferred embodiment, the invention isimplemented in software, which includes but is not limited to firmware,resident software, microcode, etc.

Furthermore, the invention can take the form of a computer programproduct accessible from a computer-usable or computer-readable mediumproviding program code for use by or in connection with a computer orany instruction execution system. For the purposes of this description,a computer-usable or computer readable medium can be any apparatus thatcan contain, store, communicate, propagate, or transport the program foruse by or in connection with the instruction execution system,apparatus, or device.

The medium can be an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system (or apparatus or device) or apropagation medium. Examples of a computer-readable medium include asemiconductor or solid state memory, magnetic tape, a removable computerdiskette, a random access memory (RAM), a read-only memory (ROM), arigid magnetic disk and an optical disk. Current examples of opticaldisks include compact disk-read only memory (CD-ROM), compactdisk-read/write (CD-R/W) and DVD.

A data processing system suitable for storing and/or executing programcode will include at least one processor coupled directly or indirectlyto memory elements through a system bus. The memory elements can includelocal memory employed during actual execution of the program code, bulkstorage, and cache memories which provide temporary storage of at leastsome program code in order to reduce the number of times code must beretrieved from bulk storage during execution.

Input/output or I/O devices (including but not limited to keyboards,displays, pointing devices, etc.) can be coupled to the system eitherdirectly or through intervening I/O controllers.

Network adapters may also be coupled to the system to enable the dataprocessing system to become coupled to other data processing systems orremote printers or storage devices through intervening private or publicnetworks. Modems, cable modem and Ethernet cards are just a few of thecurrently available types of network adapters.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A method, comprising: applying a current to alead of a tunneling magnetoresistance sensor for inducing joule heatingof the lead or a heating layer, the level of joule heating beingsufficient to anneal a magnetic layer of the sensor; and maintaining thecurrent at the level for an amount of time sufficient to anneal thetunneling magnetoresistive (TMR) sensor, wherein no external magneticfield is applied to the sensor during application of the current.
 2. Amethod as recited in claim 1, wherein the lead is also a lead used forapplying a sense current to the sensor.
 3. A method as recited in claim1, wherein the lead is not used for applying a sense current to thesensor when the current is applied to the lead.
 4. A method as recitedin claim 1, wherein the current does not pass through the magnetic layerwhen the current is applied to the lead.
 5. A method as recited in claim1, wherein the current is applied in a drive having the sensor installedtherein.
 6. A method as recited in claim 5, wherein the drive is a tapedrive.
 7. A method as recited in claim 5, wherein the drive is a harddisk drive.
 8. A method as recited in claim 1, comprising applying asecond current to a second lead of the sensor, the second lead beingpositioned on an opposite side of a tunnel junction layer of the TMRsensor as the lead, the second current reducing a voltage differentialacross the magnetic layer.
 9. A method, comprising: determining acurrent level and a current application duration, the current level anda current application duration being able to induce joule heating at alevel sufficient to anneal a magnetic layer of a tunnelingmagnetoresistive (TMR) sensor into a recovered state; applying a currentat the current level to a lead of the TMR sensor; and maintaining thecurrent at the current level for the current application duration,wherein no external magnetic field is applied to the sensor during thecurrent application duration, wherein the current does not pass throughthe magnetic layer when the current is applied to the lead.
 10. A methodas recited in claim 9, wherein the lead is also a lead used for applyinga sense current to the sensor.
 11. A method as recited in claim 9,wherein the lead is not used for applying a sense current to the sensorwhen the current is applied to the lead.
 12. A method as recited inclaim 9, wherein the current is applied in a drive having the sensorinstalled therein.
 13. A method as recited in claim 9, wherein the driveis a tape drive.
 14. A method as recited in claim 9, wherein the driveis a hard disk drive.
 15. A method as recited in claim 9, furthercomprising applying a second current to a second lead of the sensor, thesecond lead being positioned on an opposite side of a tunnel junctionlayer of the TMR sensor as the first lead, the second current reducing avoltage differential across the magnetic layer.
 16. A method as recitedin claim 9, wherein the level of the current is between 1 mA and 100 mA,wherein the current application duration is between 30 seconds and 5hours.
 17. A method, comprising: characterizing thermodynamic parametersof a tunneling magnetoresistive (TMR) sensor; using the characterizedthermodynamic parameters to determine a current level and a currentapplication duration, the current level and a current applicationduration being able to induce joule heating at a level sufficient toanneal a magnetic layer of the sensor into a recovered state;characterizing thermal characteristics of the TMR sensor; applying acurrent at the current level to a first lead of the TMR sensor while asecond lead, coupled to the first lead, is coupled to ground; andmaintaining the current at the current level for the current applicationduration, wherein no external magnetic field is applied to the sensorduring application of the current.